Sonia Meller

Forests dominated by beech (Fagus sylvatica L.) cover large parts of Europe where they occupy a broad ecological niche in terms of soil fertility. This indicates a large potential to adapt to different soil conditions over long time periods. Recent changes in tree mineral nutrition across Europe raise the question to what degree beech can acclimate to changing soil conditions in the short term. In this study, we aimed at assessing the plasticity of root traits and rhizosphere properties of young beech trees from populations that are adapted to either high or low nutrient supply, when growing in soils differing in their fertility. We sampled beech saplings from two forest sites of contrasting nutrient supply, most distinctly in terms of phosphorus. We grew them for 2 years in rhizoboxes in mineral soil either from their own site or from the other site. We assessed the influence of the factors "plant origin" and "current soil" on root traits and rhizosphere properties. Fine root traits related to growth (biomass, length), architecture (branching), and morphology (diameter) responded strongly to the factor “current soil.” Provenance (factor “plant origin”) modified the response. The modifying effect was consistent with an influence of the plant status in those nutrients, which were not in sufficient supply in the soil. An additional genotypic difference in the sensitivity of the beech saplings to different soil nutrient supply could not be excluded. Fine root parameters normalized for length, mass, or volume (root tip density and frequency, specific root length and area, and root tissue density) did not differ among the treatments. Differences in percentage of mycorrhizal root tips and rhizosphere parameters related to phosphorus mobilization potential (pH, abundance of organic acid anions, and phosphatase activity) were small and mainly determined by the “current soil.” Provenance had only a minor modifying effect, possibly due to differences in the ability of the plants to transfer carbon compounds from the shoot to the root and the fungal partner. Our results indicate a high plasticity of young beech trees to adapt their root system to different soil nutrient supply, thereby also taking into account internal nutrient reserves.

Decreasing phosphorus (P) concentrations in leaves of beech (Fagus sylvatica L.) across Europe raise the question about the implications for forest health. Considering the distribution of beech forests on soils encompassing a broad range of nutrient availability, we hypothesized that this tree species exhibits high phenotypic plasticity allowing it to alter mass, and nutrient allocation in response to local nutrient availability. To test this,
we grew two groups of 12–15 year old beech saplings originating from sites with high and low soil P availability for 2 years in mineral soil from their own site and in soil from the other site. After two growing seasons, P concentrations in leaves and stem, as well as mass allocation to leaves and fine roots were affected by both soil and plant origin. By contrast, relative P allocation to leaves and fine roots, as well as P concentrations in
fine roots, were determined almost entirely by the experimental soil. Independent of the P nutritional status defined as average concentration of P in the whole plant, which still clearly reflected the soil conditions at the site of plant origin, relative P allocation to leaves was a particularly good indicator of P availability in the experimental soil. Furthermore, a high plasticity of this plant trait was indicated by a large difference between plants
growing in the two experimental soils. This suggests a strong ability of beech to alter resource allocation in response to specific soil conditions.

Forests dominated by beech (Fagus sylvatica L.) cover a large part of Europe and occur on a wide variety of soils, realizing a broad ecological niche in terms of soil chemical properties including pH, base saturation, and plant-available phosphorus (P) pools in the mineral topsoil. On the other hand, a decrease in foliar P concentrations and a corresponding increase in the nitrogen (N) to P ratio during the last decades all over Europe raised questions about a possible reduction in forest health and productivity due to P limitation. These changes in leaf nutrient status have been attributed to continuing high N deposition and increasing atmospheric carbon dioxide concentrations. Both accelerated tree growth due to high N and carbon (C) input and adverse effects of elevated N on fine root biomass, mycorrhization, and litter mineralization appear to have created a higher need for other nutrients that cannot be met by the supply from the soil. Surprisingly little is known about internal P allocation of beech and its capacity to deal with changing soil P availability in the short-term. Considering the distribution of beech forests on soils encompassing a broad range of nutrient availability, and thus proven ability to adapt to different soil conditions in the long-term, we hypothesized that this tree species exhibits a high phenotypic plasticity allowing it to alter multiple traits in response to local nutrient availability leading to adaptive acclimation and resulting in a phenotype tailored for local soil conditions. [...]

Buchenwälder (Fagus sylvatica L.) bedecken grosse Teile Europas und kommen auf einer Vielzahl von Böden vor, die einerseits eine breite ökologische Nische in Bezug auf bodenchemische Eigenschaften wie pH-Wert, Basensättigung und pflanzenverfügbaren Phosphor (P) im Oberboden bilden. Andererseits haben in Europa zurückgehende P Gehalte in Blättern und der damit einhergehende Anstieg des Stickstoff (N) zu P Verhältnisses während der letzten Jahrzehnten die Frage über einen möglichen Rückgang der Waldgesundheit und der Produktivität aufgrund von P Limitierung aufkommen lassen. Diese Veränderungen im Nährstoffgehalt der Blätter wurden hauptsächlich auf anhaltend hohe N Depositionen und ansteigende atmosphärische CO2 Konzentrationen zurückgeführt. Sowohl beschleunigtes Baumwachstum durch hohe N und Kohlenstoff (C) Einträge als auch negative Effekte von erhöhtem N auf die Feinwurzelbiomasse, die Mykorrhizierung und die Streumineralisierung scheinen einen höheren Bedarf an anderen Nährstoffen ausgelöst zu haben, der nicht durch die Versorgung aus dem Boden gedeckt werden kann. Erstaunlicherweise ist sehr wenig bekannt über interne P Zuteilung in Buchen und deren Kapazität mit veränderter Phosphorverfügbarkeit im Boden auf kurze Sicht zurecht zu kommen. [...]